Generally, a cutting insert is fastened to a cutting tool mounted on a machine tool and used for cutting a workpiece that is generally formed of ferrous or nonferrous metals, non-metal material, and so on.
An example of such cutting insert is disclosed in Korean Registration Patent No. 10-0988410.
Referring to FIGS. 8 to 11, a related cutting insert will be described. For reference, FIGS. 8 to 11 each correspond to FIGS. 1, 4, 3 and 7 of KR10-0988410, and the same reference numerals are used for convenience of explanation. Further, the same names of the elements are used as used in KR10-0988410.
Such related cutting insert is a tangential milling cutting insert 10 for use with a milling cutter, which has two opposed identical end surfaces 12 having two opposed identical major side surfaces 18, generally in a shape of parallelogram, and two opposed identical minor side surfaces 16 extending therebetween. Each of the end surfaces 12 includes a peripheral edge 54 including a cutting edge 52, and four corners of two diagonally-facing upward corners 24 and two diagonally-facing downward corners 26. Each of the end surfaces 12 is provided with a junction member 28 having a junction surface 30.
Meanwhile, the related cutting insert adopts double-sided type, and a major side surface 18 and a minor side surface 16 are perpendicular to each other. Therefore, fastening with a holder can be relatively less secure (see FIGS. 10 and 11A).
Further, as illustrated in FIG. 11, there is a limit to providing a large axial rake angle of the peripheral edge 54 and thus, enhancement of the cutting characteristics is also limited.
Further, as illustrated in FIG. 8, when fastening with the cutting tool, the presence of the rake surface 60 formed on the end surface 12 serving as a fastening surface results in a decreased fastening area and therefore, fastening with the cutting tool is deteriorated.
Further, as illustrated in FIG. 9, the size of the cutting insert is considerably increased, in which case the number of cutting inserts that are applicable for use with the milling cutter with the same machining diameter is limited, and the machining productivity is deteriorated.
In particular, the related double-sided cutting insert uses a portion (i.e., inner end surface 46) of the end surfaces 12 (upper and lower surfaces) as a fastening surface, and uses the other as an inclined surface (i.e., rake surface 44) to discharge chips (see paragraphs [0044] and [0047] of KR10-0988410 for reference). Accordingly, the surface area of the fastening surface for fastening with the milling cutter body is narrow, and considerable problem occurs (e.g., breakage of the fastening screw passed through the cutting insert and fastened into the milling cutter body, which can occur during high-speed high-stiffness machining, generation of vibration during cutting process, or the like).
Further, when set in the cutter body such that the upper surface is used as the rake surface, the lower surface is used as the fastening surface. Alternatively, when the lower surface is used as the rake surface, the upper surface is used as the fastening surface. This relationship causes problem such as deteriorated performance due to limits in the designing of rake surface for chip evacuation, designing of helix angles, and so on.
Meanwhile, in an example of a flat-shaped insert in which a side surface is formed as a positive surface, since the side surface serving as the fastening surface is formed as a positive surface, constraining force is decreased after fastening with the cutter body, and problem of vibration occurs due to cutting impact during cutting process.